The present invention relates to valves for controlling fluid flows. In particular, the present invention relates to a valve for proportionally controlling a fluid flow using a shape memory alloy as an actuator for opening and closing the valve.
Valves and other types of flow control systems are commonly used in a variety of different types of applications for controlling the flow of various fluid materials through flow lines. Such different types of valves include needle valves, spool valves, butterfly and pinch valves, among others. Generally, such valves will include a body or housing through which a flow passage is defined and having a valve element mounted along the flow passage and which is movable between an open and a closed position for opening and closing the flow passage to restrict the fluid flow therethrough. For example, most pinch valves generally are mounted along a flexible flow line and include one or more movable pinch jaws that are moved or closed together to engage the flow line therebetween to pinch or shut off the fluid flow through the flow line.
In the past, most conventional valves typically have been mechanically actuated or, more recently, electromechanically actuated such as by use of a solenoid. Such solenoid actuated valves are, however, generally limited to being on/off type valves in which the valve elements are moved either to a fully open or fully closed position. In many fluid dispensing applications, such as medical or pharmaceutical applications, where control of the amount of fluid being dispensed is important and in some cases critical, however, it is desirable for the actuation of the valves to be controlled or regulated so that the valves can be closed by a desired amount to precisely and proportionally regulate the fluid flow therethrough as desired. In addition, such electromechanically actuated valves generally are relatively cumbersome and expensive and are not readily replaceable or disposable, or require their actuator, i.e., a solenoid, to first be disconnected and removed before discarding the valve assembly.
More recently, other types of actuators have been used for controlling the actuation of flow control valves. For example, U.S. Pat. No. 4,973,024 of Homma discloses the use of a shape memory alloy (SMA) for moving a valve element between open and closed positions to open and close a valve port. Shape memory alloys generally are metal alloy wires that tend to contract in response to heating of the alloy by application of an electric current therethrough. Thereafter, as the alloys cool back to room temperature, they are easily stretched back to their normal length. The contracting force of the alloys further exerts significant pulling force and is used in Homma for moving a valve element out of engagement with a valve port to open the valve port.
One problem with such shape memory alloys is that the strength or force exerted by the alloy is dependent upon the size of the alloy wire used such that a thicker alloy wire is required for greater compressive strength. However, as the size of the alloy (i.e., the thickness of the wire) is increased, the reaction time of the alloy, and thus the timing of the opening and closing of the valve, generally decreases without application of significantly increased current, potentially impairing the performance of the valve. Thus, such shape memory alloys may not be practical for use in some applications where precise proportional control of a fluid flow is required.
Accordingly, it can be seen that a need exists for a proportional flow control valve that is able to address these and other related and unrelated problems in the art.
Briefly described, the present invention relates to a proportional flow control valve for controlling the flow of a fluid through a fluid flow line at desired levels or rates of flow. Typically, the valve will be mounted along a fluid flow line at an intermediate position therealong, and generally includes a body or housing generally that typically is formed from a rigid, durable material such as a plastic or metal material. The valve body or housing includes a base portion that defines an inner valve chamber, and an upper plate or cover that is mounted over the base for enclosing the valve chamber.
A flow passage is defined through the valve body, through which a flexible flow tube is received. Typically, the flow tube will be formed from a flexible plastic material or similar compressible, resilient material and includes a coupling or connector at each end for connection to the fluid flow line. The fluid is received and flows through the flow tube, which is typically compressed or squeezed within the valve as necessary to restrict or control the fluid flow therethrough. In addition, the flow line itself can be formed from a flexible, compressible tubing material that is extended through the valve passage without requiring the use of a flexible flow tube.
The valve further includes a valve assembly mounted within the chamber of the valve body and including one or more valve elements that engage and pinch or squeeze the flow line to restrict and control the fluid flow therethrough. In a first embodiment of the valve, the valve elements generally include pinch jaws mounted along the flow tube. The pinch jaws generally include at least one active jaw that is movable toward and away from the flow tube, engage and compress the flow tube between the pinch jaws to restrict the fluid flow. A biasing element generally is attached to at least one of the pinch jaws for biasing the pinch jaw(s) to a normally open or closed rest position depending upon the biasing for the particular application in which the valve is being used.
A valve actuator is mounted within the valve body for moving the valve elements into engagement with the flow tube/flow line. The valve actuator comprises at least one shape memory alloy element typically in the form of a wire or flat strip. The shape memory alloy element is connected to a power supply that supplies an electric current to heat the shape memory alloy element. In response, the shape memory alloy element contracts, exerting a moving or pulling force against at least one of the jaws for moving the pinch jaw(s) between open and closed positions. As the flow of current is halted and the shape memory alloy element cools, the biasing element biases the pinch jaw(s) back to a rest position.
A pulley system is mounted within the valve chamber and includes a series of pulley members about which the shape memory alloy element is extended so as to increase the strength/moving force applied to the active pinch jaw by the shape memory alloy element by between typically 2:1 up to 4:1 or greater. This enables the shape memory alloy wire to be of reduced dimensions with increased or enhanced strength and reaction times. In addition, multiple shape memory alloy elements (i.e., two or more) typically are used, generally extended in parallel to provide additional pulling force with faster reaction times and to reduce incidences of potential failure of the valve if one of the shape memory alloy elements breaks.
In an additional embodiment of the valve, the stationary pinch jaw of the first embodiment is replaced with a removable jaw received within a longitudinally extending channel within the valve body. The removable jaw has a substantially rectangularly shaped body including an upper portion having a bearing surface against which the flow tube is compressed, and resilient leg members that project downwardly. Locking tabs are formed along the leg members, projecting outwardly and engage corresponding locking recesses formed in the body of the valve. The tabs are held in locking engagement with the recesses by the resilient leg members bearing against the valve body to lock the removable jaw plate in a fixed position within the valve body.
In use, the leg members are urged inwardly to release the locking tabs from the locking recesses and enable the jaw plate to be removed from the valve body. Thereafter, the valve body is fitted over the flow line, with the flow line received within the flow passage. The removable jaw is then reinserted into the valve.body and is moved into engagement with the flow tube, with its locking tabs being engaged within the locking recesses of the valve body.
In a third embodiment of the valve, the valve body is formed with an internally mounted flow tube that defines a flow passage and includes connectors at each end for connecting the valve to the flow line. In this embodiment, the valve elements include a movable pivot arm having a pinch roller mounted thereto, and a stationary support or bearing plate below the flow tube. The pivot arm is connected at one end to a biasing element, generally a compression or tension spring, which biases the pinch arm toward a normally open or normally closed position. The valve actuator comprises a shape memory alloy element extended about a pulley system mounted within the valve body and connected to a power source which communicates with the ends of the shape memory alloy element for supplying an electrical current thereto. In response, the shape memory alloy element contracts so as to exert a moving/pulling force on the second end of the pivot arm to cause the pinch roller to either engage the flow tube between the pinch roller and bearing plate, or be moved away from the bearing plate to allow the flow tube to decompress, for restricting or opening the flow tube to control the fluid flow therethrough as desired.
In an additional embodiment of the valve, the support or bearing plate of the third embodiment can be replaced with a second pivotable pinch arm. In such an embodiment, the opposed pinch arms typically each include a first end at which a pinch roller is mounted, a second end connected to the biasing element and having a pulley member attached thereto, and about which the shape memory alloy element is extended, and a pivot pin mounted at an intermediate portion along the length of the pinch arm and about which the pinch arms are pivoted toward and away from engaging, contact with the flow tube upon actuation of the shape memory alloy element.
In a further embodiment of the valve, the valve body is formed from a pair of opposed clamping arms that are pivotally mounted about a common pivot pin. Each clamping arm generally includes a first or proximal end and a second or distal end, with the proximal ends of each arm biased together by a biasing element such as a main spring. A recess is formed within each of the clamping arms adjacent their first or proximal ends, so as to define a passage through which the flow line is received. Pinch jaws are mounted to each of the clamping arms adjacent their proximal ends, and are movable into the flow passage. A shape memory alloy element is extended about a pulley system mounted within each of the clamping arms and each pinch jaw. As current is applied through the shape memory alloy element, the shape memory alloy element contracts and urges the pinch jaws toward a closed position with the flow line engaged therebetween for restricting the flow of fluid through the flow line.
The valves of the above discussed embodiments generally are connected to external or internal power supplies for supplying an electrical current to the shape memory alloy element. The valve also typically includes a control system for delivering power to the shape memory alloy element(s) to actuate the valve. The control system generally will include a driver circuit for modulating the power supplied to the shape memory alloy element. The driver circuit typically is linked with a programmable controller that monitors the valve and controls the power to the shape memory alloy element and can be linked to or be part of a feedback control, which measures internal resistance of the shape memory alloy element, or which can include an internal valve sensor that measures the position of the pinch jaw(s) or external feedback sensors, such as a flow-meter, that measure the amount of flow through the flow line. In response, the controller can adjust the current applied to the shape memory alloy to adjust the opening/closing of the valve to achieve a desired rate of flow.
Various objects, features and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description when taken in conjunction with the accompanying drawings.